Linear vibration welding devices are known in which the thermoplastic components are placed on a bed wherein the movement described is reciprocating translation in a preferred direction. The bed is generally moved by hydraulic or electromagnetic means powered by an AC voltage; nevertheless, these devices, owing to the kinematics which they have to impart to the component to be welded, require that at a given moment corresponding to an extremum in the trajectory, the speed of the moving body, which was non-zero and of given amplitude and direction a few minutes beforehand, cancels out, changes direction, and reaches a similar amplitude in terms of absolute value to the previous one, which involves variations in the operation and energy usage of the device; a fraction of the energy expended is downgraded as the bed slows down, and this results in heterogeneity of the weld bead, the fusion temperature reached not being uniform along the weld bead especially when the latter is not orientated in a direction parallel to the movement of travel of the bed.
The present invention therefore aims to overcome these drawbacks by providing a device which makes use of the advantages of the modes of orbital vibration; indeed, according to this mode of vibration, the modulus of the speed remains practically constant over the entire trajectory, the changes in direction taking place progressively and continuously; moreover, this mode of vibration allows complex trajectories combining planar rotation and translation-best corresponding to the convolutions of the joining lines.
For this purpose, the device for causing epicycloid vibration is characterized in that it comprises at least one shaft secured by one of its ends to a bed connected by elastic means to the frame of the machine and furthermore supporting a thermoplastic component, the said shaft being provided at this end with a magnetic mass, which when made to rotate inside a plurality of magnetic fields brought about by switching on a plurality of electromagnets located about the said shaft, generates an orbital-type movement of the bed, the other free end of the shaft being, on the one hand, guided in rotation within the frame of the machine and, on the other hand, driven in rotation by a motor.